1. Field of the Invention
The present invention relates to a copier, printer, facsimile device, or other image-forming device, and particularly relates to a bulk paper feeding device having an intermediate conveyor for feeding paper to an image-forming device.
2. Description of the Background Art
Among copiers, printers, facsimile devices, and other image forming devices, an image forming device such as a printer, especially a stencil printer or offset printer, is suited for use in printing based on a plate created from a single original sheet, and large-volume printing from a single original sheet often involves printing several thousand sheets because, unlike a copier or the like, such a device uses the original image plate.
A bulk paper feeding device having an intermediate conveyor capable of feeding a large quantity of paper on which an image is to be formed by this type of printer or other image forming device is known, and an example thereof is depicted in FIGS. 1 through 6 of U.S. Pat. No. 5,441,247. This bulk paper feeding device having an intermediate conveyor is equipped with a carrier capable of carrying a large quantity of paper, a paper feeding mechanism for picking up and feeding one sheet at a time of the paper from the carrier, and an intermediate conveyor for transporting a sheet of paper fed from the feeding mechanism to the main paper feeding table of the paper feeder on the body of the printer. Placing a raisable intermediate conveyor on the main paper feeding table of the printer allows a paper sensor (reflecting photosensor) for detecting the presence of paper, mounted on the main paper feeding table, to be shielded, indicating that paper is present. In this state, a sheet of paper is picked up from the carrier by the paper feeding mechanism, the paper is transported by the intermediate conveyor to an appropriate position (under the main paper feeding roller) from which paper can be fed to the printer body, and the paper is then stopped.
After an operator, user, or the like (hereinafter referred to as “operator”) confirms that the paper has been transported and stopped in the appropriate position, specifically, under the main paper feeding roller, the operator presses a print button corresponding to a plate-making switch or printing switch mounted on the printer body, whereupon the control device for the printer body assumes that paper is present on the main paper feeding table based on the signal indicating that the intermediate conveyor is covering the paper sensor on the main paper feeding table, and elevates the main paper feeding table until a correct-height sensor (transmission photosensor) is activated for detecting the height at which paper can be fed at the feed pressure of the main paper feeding roller, and the intermediate conveyor is elevated together with the elevation of the main paper feeding table while tilted via its attachment to the bulk paper feeding device. A standby mode (state in which paper can be fed) occurs when the correct-height sensor is activated, the paper on the intermediate conveyor is taken in to the printing body, and printing begins.
In keeping with recent increases in the speed of printers and copiers, this bulk paper feeding device having an intermediate conveyor as described in U.S. Pat. No. 5,441,247 is prepared for the production capability of such printers and copiers, and can be applied to various machines, is mobile, and has large storage capacity for paper.
However, this conventional bulk paper feeding device having an intermediate conveyor has such drawbacks as are described below.
(1) It is concluded that paper is present in the printer body and printing is initiated if the print button on the printer body is pressed when paper is not being fed to the intermediate conveyor, but since paper is not being fed, a paper feeding jam is determined to have occurred. Because of this, correcting the problem takes time because the operator cannot determine why the paper feeding jam occurred. In addition, mistakes in the operating procedure are more likely to occur because the operator is always changing, and since the printer cannot be operated properly when the operating procedure is not correctly followed, it is required that the operator be trained for the machine, and a great deal of skill is involved.
(2) When paper is no longer being fed to the carrier and intermediate conveyor during printing, paper jamming occurs because the absence of paper cannot be recognized by the printer body, or, specifically, because an offline state occurs in which there is no exchange of electrical signals between the printer and the bulk paper feeding device having an intermediate conveyor.
(3) After the print button is pressed, the intermediate conveyor is elevated while tilted, and printing becomes possible only after the correct-height sensor is activated, so some waiting time elapses while the main paper feeding table is elevated.
(4) When a dedicated bulk paper feeding table or conveyor device is connected to a direct shipping machine, an electrical connection must be established with the printer body, requiring that the wiring or exterior cover be disassembled and making this on-site conversion extremely inconvenient. Also, mistakes in wiring connections lead to serious problems, and the danger of electrocution gives this operation the potential for extreme danger.
(5) Because only paper of a size whose length is determined by the paper transport direction can be transported, the usage range of the paper becomes limited. Therefore, such a system cannot be used by a user of a stencil printer (hereinafter referred to as (stencil printer) that uses particularly varied paper sizes, including a copier, for example.
(6) Because printing cannot be performed except on paper whose size has a length determined as described in (5) above, there is no need to differentiate paper sizes. However, in a bulk paper feeding device with an intermediate conveyor that is compatible with various paper sizes, control for maintaining the distance between sheets during transport is simplified if the paper sizes can be differentiated. It becomes possible to maintain the distance between sheets without differentiating the paper size by increasing the number of sensors for detecting the trailing edge of the sheet in front transported earlier (hereinafter referred to as “front sheet”) and the leading edge of the next transported sheet, but control in this arrangement is complex. Because of the resultant increase in cost, it is preferred that control be performed with as few sensors as possible.
(7) In order to achieve the object described in (6) above, it may be possible to mount a sensor on the carrier that would be equivalent to a paper length sensor for differentiating the length of the paper being used by the paper feeding table of a printing device or the like, but such a configuration would be complex and arranging the sensor wiring would be difficult, leading to increased cost. Also, the paper length sensor can classify paper only into two types of sizes above and below A4 transverse size.
(8) When accommodating printing speeds from a particularly low speed (16 rpm when versioning, for example) to the maximum speed (120 rpm, for example) such as with a stencil printer, for example, the subsequent sheet overtakes the front sheet transported at a low speed and drawbacks occur whereby both sheets are damaged, the sheets deform and jam, and not all speeds for paper feeding can be accommodated. Among printers, a large variety of papers are used in stencil printers in particular. Paper is generally classified as standard, thin, or thick, but because the. standard paper used regularly for bulk paper feeding itself includes high quality (high quality 55 kg paper, high quality stencil paper, and the like), medium quality, recycled paper, and the like, the conventional arrangement is not compatible with these papers.
(9) Because there is no one-way clutch attached to the transport roller of the intermediate conveyor, when using a thin paper whose surface has a comparatively large frictional coefficient, for example, a resistant load against paper transport is created during rotation of the paper feed roller, also known as the paper feed roll, in the body of the image forming device (hereinafter referred to as “device body”), leading to inadequate paper transport and possible jamming. Specifically, after it is confirmed that the paper has moved by the rotation of the paper feed roller of the device body, rotation starts for the transport roller of the intermediate conveyor located under the paper feed roller of the device body, making it difficult initially for the transport roller to rotate because of the load on the electric motor for rotatably driving the transport roller.
(10) Because guiding members for guiding the paper over the intermediate conveyor are mounted only in certain locations, the conventional bulk paper feeding device with an intermediate conveyor is not suited for transport of paper with inconsistent quality, in which there are wide variations in stiffness, such as groundwood paper, because with thin paper such as groundwood paper that has no stiffness (strength represented by flexural rigidity), the leading edge of the paper catches on protrusions (which characterize the jaggedness of the surface) on the paper feed roller of the device body, prompting tearing of the leading edge of the paper, paper damage, and jamming. The conventional approach is not compatible with stencil printers, in particular among printers.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Application Laid-open Nos. S59-124633, H8-67061, H8-259008, H8-259009, H10-45268, 2002-226122, and 2002-326732, and in Japanese Utility Model Publication No. H5-18342.